Its recent decision to lock out third-party ad networks, combined with its clear move in to the edge application space fundamentally alter what Twitter is. It is no longer a platform for application developers to productize around core stream functionality and monetize the edge of the Twitter network. No, if Twitter wanted to be a platform, it would keep its business focused on inspiring innovation on the edge of its network, managing the infrastructure and monetizing the stream.

Truth is, Twitter never was a platform. It has always been a consumer facing application. It is hard (perhaps impossible) to be both a consumer facing application and a platform. A true platform is a true complement with application developers. But a consumer facing application business is a pure competitor with application developers. Because Twitter hasn’t been able to sufficiently monetize the raw stream, it had no choice but to move up stack into the application and monetization layers of its value-chain. I don’t blame Twitter for moving in this direction; it’s totally logical and it was foreseeable.Tacky to quote myself, but in a prior blog post I said:

If you are an application developer on a consumer-facing platform, be sure the platform you build upon has a clear business model for helping you monetize the relationship you develop with the consumer. If not, be wary; what you do may eventually be consumed back into the platform. You may be left with no strategy for monetizing the user base you help to create.

So what is Twitter? Well, lets call it what it is – a consumer application – and a big, but narrow one at that. In the end, that is all it ever was.

I don’t have a dog in this hunt; I have not invested in any Twitter application developers for fear of the very outcome that has transpired – Twitter vertically integrating into apps and monetization with scale. I’m just a student of the platform strategy game. The lesson learned here should be noted by application developers on any consumer-facing “platform”. Be wary unless your platform is a pure complement.